The present invention relates to a process for cooling water and a cooling tower.
There has been more and more demand for cooling towers for cooling water used in large quantities in various plants, factories, buildings and the like.
A conventional cooling tower as shown in FIG. 1 has an outlet 3 with an axial flow fan 2 at a top of a casing 1, air inlets 4 at an outer periphery of the casing 1, an upper water vessel 5 at the upper portion of the casing 1 and a heat exchanger 9 below the water vessel 5 in which water 7 to be cooled is sprayed through spray ports 6 of the vessel 5 and is heat-exchanged in a cross flow manner with ambient air 8 sucked transversely into the casing 1 through the air inlets 4, thereby cooling the water 7.
The heat exchanger 9 may have a dry type air heating unit 11 in the form of finned tubes 10 immediately below the water vessel 5 and a filler unit 12 in the form of a number of heat transfer surface members with irregular surfaces, made of sheet-like synthetic resin and arranged in parallel with each other to define flow passages or in the form of assembled sheet-like members. Reference numeral 13 denotes a lower water vessel below the filler unit 12 to recover the cooled water.
With the cooling tower of the type described above, the water 7 flows down through the finned tubes 10 of the dry type air heating unit 11 and then over the heat transfer surface members of the filler unit 12 while the ambient air 8 is sucked through the inlets 4 and is directed to flow transversely of the units 11 and 12, thereby cooling the water 7.
The water 7 flowing down along the heat transfer surface members of the filler unit 12 is directly heat-exchanged with the ambient air 8 and is effectively cooled. Ability or capability of a cooling tower is substantially dependent upon volume of the filler unit 12. The air 8 having been heat-exchanged with the water 7 in the filler unit 12 becomes wet air 14 which has a high temperature and a moisture content of substantially 100%. If the wet air 14 were directly discharged out of the cooling tower, it would become white smoke when the ambient temperature is low. Such white smoke will be abhorred by the neighborhood since it seems as if the white smoke would contaminate their environment. Moreover, there is a fear that the white smoke may be erroneously regarded as a fire at night due to optical illusion or the like. Thus, the demand for preventing white smoke from being generated is increased.
To this end, in the cooling tower as shown in FIG. 1 with the water 7 flowing down through the finned tubes 10, the ambient air 8 flowing along outer peripheral surfaces of the tubes 10 is heated in dry manner into dry air 15 having an extremely low moisture content. The dry air 15 is mixed with the wet air 14 by the fan 2 to reduce the moisture content of the air to be discharged through the outlet 3, thereby preventing the white smoke from being generated.
Such a cooling tower, which is provided with the dry type air heating unit 11 in the form of the finned tubes 10 exclusive for generating the dry air 15 for prevention of the white smoke from being generated, is much complicated in structure and highly expensive in production cost. Because of indirect heat exchange by the finned tubes 10, the heat exchange efficiency cannot be satisfactorily enhanced and in compensation therefor the dry type air heating unit 11 is increased in size. It follows therefore that if the filler unit 12, which is a major cooling part, is not changed in volume, the cooling tower must be increased in height or volume and if the cooling tower is not changed in height or volume, the filler unit 12 must be decreased in volume and the cooling efficiency drops.
In order to overcome these problems, a cooling tower as shown in FIGS. 2 and 3 has been proposed in which the heat exchanger 9 comprises at least two stacks of or upper and lower filler units 16a and 16b. The uppermost filler unit 16a has heat exchange surface members 17 with irregular surfaces and made of sheet-like synthetic resin which extend in parallel with each other to define flow passages 18. Some of the flow passages 18 are closed at their tops with caps 19 so that the water 7 is prevented from flow down through the closed flow passages 18. If need be, the caps 19 may be of opening and closing type. Reference numeral 20 denotes an intermediate water vessel.
Since the caps 19 are provided for closing some flow passages 18 as described above, not the water 7 but only the ambient air 8 flows down through the closed flow passages 18 to produce the dry air 15. The dry air 15 is mixed with the wet air 14 which has cooled the water 7 at the non-closed flow passages 18 in the upper filler unit 16a and at the the lower filler unit 16b and the mixed air is discharged, thereby preventing the white smoke from being generated.
With the caps 19 being of opening and closing type as mentioned above, all the caps 19 may be opened to make the water 7 flow down over all of the heat exchange surface members 17 to thereby maximize the cooling capability of the filler units 16a and 16b.
However, such caps 19 have drawbacks. If the caps 19 are securely attached to the upper ends of some flow passages 18, there always remain spaces in the upper filler unit 16a for producing the dry air even upon use of the cooling tower in a condition of no white smoke being generated, which accordingly lowers the cooling capability of the cooling tower.
With the caps 19 being of opening and closing type, the operation of closing or opening the caps 19 is cumbersome. Because of the heat exchange surface members 17 being made of sheet-like synthetic resin for lightness in weight and arranged in a narrow spaced-apart relationship, it becomes technically very difficult to install the caps 19 for opening and closing at upper ends of the flow passages 18 defined by thin synthetic resin sheets. Even if the caps 19 are managed to be installed at the upper ends of the flow passages 18 for closing and opening of the caps 19, its structure becomes very complicated and its maintenance becomes extremely difficult since the moving parts are at the narrow spaces. Thus, such covers 19 are impractical in use.
In view of the above, the present invention has for its object to provide a process for cooling water and a cooling tower in which, as to some flow passages in a filler unit, direct cooling of the water by ambient air can be freely and readily switched into dry type heating of the ambient air and vice versa.